Method for forming spacers on a display substrate

ABSTRACT

A method for forming spacers for a display device includes steps of contacting a substrate of one of a cathode and a faceplate substrate with a member, drawing the member from the substrate to form a filament, and detaching the member from the filament. The filament can be further planarized to a desired height and shape. The filament extends to the other of the cathode and faceplate.

GOVERNMENT CONTRACT INFORMATION

This invention was made with Government Support under Contract No.DABT63-93-C-0025 awarded by the Advanced Research Projects Agency(ARPA). The Government may have certain rights in this invention.

BACKGROUND OF THE INVENTION

The present invention relates to displays, and more particularly toprocesses for forming spacers in a field emission displays (FED).

Referring to FIG. 1, in a typical FED (a type of flat panel display), acathode 21 has a substrate 10, such as glass, on which conductive layers12, such as doped polycrystalline silicon or aluminum, are formed.Conical emitters 13 are constructed on conductive layers 12. Surroundingemitters 13 are a dielectric layer 14 and a conductive extraction grid15 formed over dielectric layer 14. When a voltage differential from apower source 20 is applied between conductive layers 12 and grid 15,electrons 17 bombard pixels 22 of a phosphor coated faceplate (anode)24. Faceplate 24 has a transparent dielectric layer 16, preferablyglass, a transparent conductive layer 26, preferably indium tin oxide(ITO), a black matrix grille (not shown) formed over conductive layer 26and defining regions, and phosphor coating over regions defined by thegrille.

Cathode 21 may be formed on a backplate or it can be spaced from aseparate backplate. In either event, cathode 21 and faceplate 24 arespaced very close together in a vacuum sealed package. In operation,there is a potential difference on the order of 1000 volts betweenconductive layers 12 and 26. Electrical breakdown must be prevented inthe FED, while the spacing between the plates must be maintained at adesired thinness for high image resolution.

A small area display, such as one inch (2.5 cm) diagonal, may notrequire additional supports or spacers between faceplate 24 and cathode21 because glass substrate 16 in faceplate 24 can support theatmospheric load. For a larger display area, such as a display with athirty inch (75 cm) diagonal, several tons of atmospheric force will beexerted on the faceplate, thus making spacers is important if thefaceplate is to be thin and lightweight.

It would be desirable to have a convenient and efficient method toaccurately form and locate spacers in a FED.

SUMMARY OF THE INVENTION

This invention includes methods for forming spacers for a display, suchas an FED, that has a cathode with a substrate and a faceplate with asubstrate. One method includes contacting one of the substrates with aheated member, drawing the heated member away from the substrate toproduce an integral filament, and detaching the member from thefilament. Another method includes steps of heating the substrate,contracting the heated substrate with a member, drawing the member awayfrom the substrate to form a filament, and detaching the member from thefilament. After either of these series of steps, the resulting filamentcan be further processed, e.g., by providing filler around the spacersand performing a planarization process that can be mechanical, chemical,or a combination of mechanical and chemical.

In another aspect, the invention includes a display that has a faceplateand a cathode, at least one of which has a number of integral spacerfilaments extending toward the other of the faceplate and cathode. Thesespacers are made from the same material as the substrate without a breakor interruption, as opposed to the same or different material attachedto the substrate.

The present invention thus provides spacers at precise locations andintegral with the substrate, and further avoids the need for forming anadhesive at one end. Other features and advantages will become apparentfrom the following detailed description, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a known FED with a faceplate, acathode, and spacers therebetween.

FIG. 2-5 are cross-sectional views illustrating steps for formingspacers according to the present invention.

FIGS. 6 and 7 are cross-sectional views of two embodiments of an FEDaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 2-5, to fabricate spacers for a display according tothe present invention, a member 30, preferably a metallic needle or rodthat has good thermal conductivity, is brought into contact with asubstrate 32 that may be used for or be part of a faceplate or acathode. Substrate 32 is preferably made of glass, so its softeningtemperature depends on the type of glass used, e.g., about 525° C. forsoda lime glass or about 650° C.-700° C. for borosilicate glass. Member30 is heated to a sufficient temperature to melt or soften substrate 32in a general area 38 of contact (FIG. 2). Member 30 may be pushedslightly below the original surface of substrate 32, e.g., severalmicrons below. It is understood that substrate 32 may be heated tofacilitate local melting or softening in a efficient and timely manner.Once this is done, member 30, which is heated, may be pushed slightlybelow the original surface of substrate 32 for purposes of making aspacer.

After localized melting or softening has occurred in area 38, member 30is drawn away from substrate 32 along a direction orthogonal to thesubstrate, thereby pulling an elongated filament 34 that extendsorthogonally from a surface of substrate 32 (FIG. 3). After filament 34has been drawn a desired length from substrate 32, preferably at leastabout 200 microns, the temperature of member 30, substrate 32, andfilament 34 is reduced so that filament 34 cools and revitrifies. Member30 is then detached from contact with filament 34 with one of severalmethods, such as drawing member 30 away, rapidly cooling member 30 andsubstrate 32, and/or ultrasonic vibration (FIG. 4).

Referring to FIG. 5, after removing member 30 from filament 34, filament34 may be surrounded and thereby supported with a polishable filler 36,such as a white wax (glycol phthalate). Filament 34 can then beplanarized to a desired height and polished flat and reduced for furtherassembly. The planarization and polishing may be performed usingconventional methods, including chemical and/or mechanical methods. Witha method of chemical mechanical planarization (CMP), a wafer ofsemiconductor material is moved relative to a wetted polishing surfaceunder a controlled chemical slurry containing a polishing agent such asalumina or silica as an abrasive medium, and with industrial gradediamonds or chemical etchants as a polishing agent.

To produce multiple filaments, the steps of contacting, drawing away,and detaching can be performed multiple times to produce filaments oneat a time before planarizing and/or polishing. Alternatively, a numberof filaments can be formed simultaneously with many members 30 (or oneassembly with multiple needles).

FIGS. 6 and 7 each illustrate displays of the field emission type havingspacers according to two embodiments of the present invention,respectively. In FIG. 6, an FED 50 has spacers 40 that extend upwardlyfrom substrate 10 of cathode 21 and contact faceplate 24, preferablywithout any adhesive. When filaments are drawn from substrate 10 ofcathode 21, it is preferred that they be drawn before additionalprocessing is done on that substrate. Accordingly, in the case of afield emission display, after filaments 40 are formed up from thesubstrate, conductive layers 12, polysilicon emitters 13, oxide layer14, and a conductive layer for forming grid 15 are formed over substrate10 with generally known techniques, and are etched according togenerally known techniques to produce the cathode as shown in FIG. 6.

The deposition and etching can be performed with the filaments alreadyformed. While spacers 40 are shown in FIG. 6 as being generallycylindrical, the filaments could be somewhat conical, particularly atthe base as shown in FIG. 5. Such a geometry is indeed desirable in theembodiment of FIG. 6 because such spacers help deflect electrons thatstrike the spacer and prevent the electrons from multiplying on thesurface of the spacer.

In FIG. 7, an FED 52 has spacers 42 that extend downwardly fromsubstrate 16 of faceplate 24 and extend to conductive extraction grid15. In this embodiment, filament spacers 42 are preferably drawn awayfrom substrate 16 prior to further processing. In this case, after thefilaments are formed and polished and after the filler is removed,conductive layer 26, a grill (not shown), and a phosphor coating (notshown) would be formed on faceplate 24 over substrate 16.

To form FED 50 or 52 as shown in FIG. 6 and FIG. 7, respectively, it maybe possible for the faceplate and cathode to be formed to a more advancestate, e.g., with conductive layers 12 or 26 already formed, and thenhave openings formed in any additional layers for the member to contactthe substrate and to draw out filaments.

In the embodiments of FIGS. 6 and 7, spacers 40 and 42 are thus formedwithout break or interruption from respective substrates 10 and 16 andwithout any intermediate layers, such as adhesive layers. Accordingly,substrates 10 and 16 substantially lie in a plane, while respectivespacers 40 and 42 extend orthogonally away from the plane in which thesubstrate lies. The end of the filaments may, but need not be, connectedby adhesion to some part of the opposing cathode or faceplate; withoutadhesive, the spacers are kept in place by the resulting pressuredifferential after sealing.

In the embodiments of FIGS. 6 and 7, faceplate 24 and cathode 21 arevacuum sealed in a package. The number of spacers and their locations inthe display will depend on their strength, and the pressure that must becounteracted.

Having described preferred embodiments of the present invention, itshould be apparent that modifications can be made without departing fromthe scope of the claims.

I claim:
 1. A method for forming a spacer for a field emission displayhaving a cathode and a faceplate, the method comprising the stepsof:contacting a substrate for the faceplate and the cathode with amember heated sufficiently to soften the substrate; drawing the memberaway from the substrate to produce a filament from the substrate;detaching the member from the filament; and assembling together thefaceplate and the cathode such that the filament extends to the other ofthe faceplate and the cathode.
 2. A method for forming a spacer for afield emission display having a cathode and a faceplate, the methodcomprising the steps of:heating a substrate for one of the faceplate andthe cathode sufficiently to soften the substrate; contacting thesubstrate with a member; drawing the member away from the substrate toproduce a filament from the substrate; detaching the member from thefilament; and assembling together the faceplate and the cathode suchthat the filament extends to the other of the faceplate and the cathode.3. The method of claim 1, further comprising the steps, after thedetaching step, of providing a filler material around the filament, andplanarizing the filament so that it has a desired height.
 4. The methodof claim 2, further comprising the steps, after the detaching step, ofproviding a filler material around the filament, and planarizing thefilament so that it has a desired height.
 5. The method of claim 1,wherein the contacting step includes contacting the substrate withmultiple members, the drawing step includes drawing away the multiplemembers to produce multiple filaments, and the detaching step includesdetaching the multiple members.
 6. The method of claim 2, wherein thecontacting step includes contacting the substrate with multiple members,the drawing step includes drawing away the multiple members to producemultiple filaments, and the detaching step includes detaching themultiple members.
 7. A method for forming a field emission displaycomprising the steps of:contacting a substrate of a cathode with amember at a contact area sufficiently heated to soften the substrate atthe contact area; drawing the member away from the substrate to from anintegral filament therefrom; forming conductive strips over thesubstrate; forming a plurality of generally conical emitters over theconductive strips; and assembling together the cathode with a faceplateso that the filament extends from the cathode substrate to thefaceplate.
 8. The method of claim 7, wherein the contacting and drawingsteps are performed to produce multiple integral filaments.
 9. A methodfor forming a field emission display (FED) comprising the stepsof:contacting a transparent faceplate substrate with a member at acontact area sufficiently heated to soften the substrate at the contactarea; drawing the member away from the substrate to form an integralfilament; forming a transparent conductive layer over the faceplatesubstrate; and assembling together the faceplate together with a cathodehaving a cathode substrate, a plurality of conductive strips, and aplurality of conical emitters formed over the conductive strips, thefaceplate and cathode being assembled with a vacuum between them. 10.The method of claim 9, wherein the contacting and drawing steps areperformed to produce multiple integral filaments.